1. Field of the Invention
The present invention relates to an optical disk reproducing apparatus which reproduces information recorded on an optical disk, and more particularly to an optical disk reproducing apparatus which has a function of calculating a time of supplying a brake signal to a spindle motor for rotating an optical disk. The present invention also relates to a method for controlling a spindle motor in which rotates an optical disk.
2. Description of the Related Art
In a conventional optical disk reproducing apparatus, a spindle motor for rotating an optical disk is controlled in the following manner. A voltage corresponding to a phase difference between a synchronization signal contained in a reproduction signal which is output from an optical pickup in a process of reproducing an optical disk, and a predetermined reference signal is produced with using a PLL (Phase-Locked Loop). The voltage is used as a motor control signal for the spindle motor.
In the case where an optical disk which is in the reproduction state and being rotated is to be stopped, even when the motor control signal for the spindle motor is simply turned off, the optical disk is not immediately stopped because of its inertial force. Therefore, a brake signal for reversely rotating the spindle motor is supplied to the spindle motor to stop the optical disk as early as possible.
An FG (Frequency Generator) sensor which generates a pulse in synchronization with the rotation of the optical disk is disposed to detect whether the optical disk is rotated or not, and detect the number of rotations of the spindle motor. When the rotation of the optical disk is to be stopped, therefore, the time of supplying the brake signal to the spindle motor is determined in accordance with the number of rotations of the spindle motor which is calculated on the basis of an output of the FG sensor. The FG sensor is configured by: a reflection sheet in which optically reflective and absorptive surfaces are alternately arranged on the lower side of a turntable on which the optical disk is placed to be rotated; and a photocoupler consisting of a light emitting device that emits light toward the reflection sheet, and a light receiving element that receives light reflected from the reflection sheet.
In Japanese Patent Publication JP-A-9-212998, a conventional brake control method for a disk player is disclosed. The method described in JP-A-9-212998 is a method that, when a braking operation is to be started, a time to elapse before the number of rotations of a spindle motor is reduced to a predetermined value is measured, and a braking time is determined on the basis of the measured time (See claim 1; column No. 0011; and FIG. 2 of JP-A-9-212998).
In the conventional optical disk reproducing apparatus, the brake signal is supplied to the spindle motor in order to stop the rotation of the optical disk. In order to determine the time of supplying the brake signal, the output of the FG sensor is required, or the FG sensor is necessary. The production cost of the apparatus is correspondingly increased, and miniaturization of the apparatus is inhibited.
In the brake control method described in JP-A-212998, the time to elapse before the number of rotations of the spindle motor is reduced to the predetermined value is measured, and the braking time is determined on the basis of the measured time. In order to detect the number of rotations of the spindle motor, a terminal of outputting a signal for detecting the rotational speed is disposed in the vicinity of the spindle motor. In the brake control method, namely, the rotational speed detection signal output terminal for detecting the number of rotations of the spindle motor is disposed, and, although not shown, an FG sensor which is to be connected to the rotational speed detection signal output terminal is necessary. In the same manner as the conventional optical disk reproducing apparatus, therefore, the production cost of an apparatus is increased by a degree corresponding to the FG sensor, and miniaturization of the apparatus is inhibited.